The present disclosure relates generally to systems and methods for imaging a subject and, in particular, to systems and methods for performing imaging processes using x-rays delivered from multiple sources.
X-ray-based imaging, including so-called “x-ray imaging” and computed tomography (CT) imaging, are some of the most common diagnostic imaging modality used in modern medicine, enabling rapid, non-invasive image acquisition at high resolution. As shown in the example diagram of FIG. 1A, conventional CT systems 10 generally include a gantry 12 fitted with a X-ray tube 14 or at most, two X-ray tubes for systems currently in clinical use and opposing detector assembly 16, which, together, rotate about a subject 18 arranged on a patient bed 20 to acquire multiple projections for reconstructing an image. That is, the X-ray tube 14 and detector assembly 16 arranged opposite the X-ray tube 14 are affixed to the gantry 12 and rotate together with the gantry 12 about the subject 18. As illustrated in the picture of FIG. 1B, this system 10 is complex and requires heavy and sophisticated control hardware and electronics.
The x-ray source 14 projects an x-ray beam 22, which may be a fan-beam or cone-beam of x-rays, towards the detector array 16 on the opposite side of the gantry 12. The detector array 16 includes a number of x-ray detector elements 24. Together, the x-ray detector elements 24 sense the projected x-rays 22 that pass through a subject 18, such as a medical patient or an object undergoing examination, who is positioned in the CT system 10. Each x-ray detector element 24 produces an electrical signal that may represent the intensity of an impinging x-ray beam and, hence, the attenuation of the beam as it passes through the subject 18. In some configurations, each x-ray detector 24 is capable of counting the number of x-ray photons that impinge upon the detector 24. During a scan to acquire x-ray projection data, the gantry 12 and the components mounted thereon rotate about a center of rotation 26 located within the CT system 10.
The CT system 10 also includes an operator workstation 28, which typically includes a display 30; one or more input devices 32, such as a keyboard and mouse; and a computer processor 34. The computer processor 34 may include a commercially available programmable machine running a commercially available operating system. The operator workstation 28 provides the operator interface that enables scanning control parameters to be entered into the CT system 10. In general, the operator workstation 28 is in communication with a data store server 36 and an image reconstruction system 38. By way of example, the operator workstation 28, data store sever 36, and image reconstruction system 38 may be connected via a communication system 40, which may include any suitable network connection, whether wired, wireless, or a combination of both. As an example, the communication system 40 may include both proprietary or dedicated networks, as well as open networks, such as the internet.
The operator workstation 28 is also in communication with a control system 42 that controls operation of the CT system 10. The control system 42 generally includes an x-ray controller 44, a table controller 46, a gantry controller 48, and a data acquisition system 50. The x-ray controller 44 provides power and timing signals to the x-ray source 14 and the gantry controller 48 controls the rotational speed and position of the gantry 12 by controlling operation of a motor 68. The table controller 46 controls a table 20 to position the subject 18 in the gantry 12 of the CT system 10.
The DAS 50 samples data from the detector elements 24 and converts the data to digital signals for subsequent processing. For instance, digitized x-ray data is communicated from the DAS 50 to the data store server 36. The image reconstruction system 38 then retrieves the x-ray data from the data store server 36 and reconstructs an image therefrom. The image reconstruction system 38 may include a commercially available computer processor, or may be a highly-parallel computer architecture, such as a system that includes multiple-core processors and massively parallel, high-density computing devices. Optionally, image reconstruction can also be performed on the processor 34 in the operator workstation 28. Reconstructed images can then be communicated back to the data store server 36 for storage or to the operator workstation 28 to be displayed to the operator or clinician.
The x-ray source 14 is a tube assembly that includes a housing unit 52, a coolant path and/or pump 54, cathode end 56, an anode end 58, and a center section 60 positioned between the cathode end 56 and the an anode end 58, which contains an x-ray tube 62. The x-ray tube 62 is enclosed in a fluid chamber 64 within lead-lined casing 66. The chamber 64 is typically filled with fluid, such as dielectric oil, but other fluids including water or air may be utilized. The fluid circulates through housing 52 to cool the x-ray tube 62 and may insulate a casing 64 from high electrical charges within the x-ray tube 62.
Though CT systems provide desirable contrast and flexibility to facilitate a wide-variety of clinical analysis, it relies upon ionizing radiation. Thus, a further constraint on the design and manufacturing of CT systems is the ability to control or adapt the dose of radiation received by the subject 18 by way of the x-ray beam 22. For example, filters, such as so-called “bowtie” filters 70, have long been utilized to sculpt the x-ray beam 22 and, thereby, control the dose received by the patient. Some filters, such as the illustrated bowtie filter 70, have been coupled with control systems and/or motors 72 to allow the filtering achieved by the bowtie filter 70 to be adjusted.
All these complex components associated with the x-ray source 14 and detector array 16 must be designed to rotate with the gantry 12. The motor 68 must be capable of applying a large torque to the large gantry 12 to accelerate the gantry 12 to a high constant rate of rotation in a short time. As an indication of the speeds which are reached, sufficient data to produce an image can be collected in less than one second. Since the rotational inertia of this apparatus increases with distance from the center of rotation 26, rotation of the gantry 12, which includes the x-ray tube 14 and detectors 16 and all associated hardware and, thus, has a large inertia, requires the motor 66 to deliver extremely high torques. Furthermore, all components of the gantry 12 must be able to withstand these forces during operation and repeated rotational starts and stops. Accordingly, CT systems are generally complex and carry very-high manufacturing and maintenance costs.
All of these and other control and programming capabilities add to the complexity and costs to these systems. As such, the trend toward greater and greater complexity of CT systems continues and, in particular, is prevalent when one considers the components and systems coupled to the gantry 12. As but one example, consider the increasing availability of dual-source CT systems. In such dual-source systems, as illustrated, the above described components associated with the gantry 12, such as the x-ray source 14, detector array 16, and the like, are doubled. Thus, the complexity of the gantry systems 12 doubles, which further increases the underlying costs of the system and the maintenance requirements.
Therefore, given the above, there is a need for systems capable of fast and accurate computed tomography imaging that is not so limited by the complexity and the costs associated with the complexity of traditional CT systems.